1. Field of the Invention
The present invention relates to dispersant materials useful for mitigating and/or inhibiting fouling of equipment used for handling and/or treating liquid hydrocarbons such as crude oil and the like, and particularly to improved antifoulant materials based on a reaction product of a hydrocarbon long chain such as polyisobutylene (PIB), a bridging agent such as maleic anhydride and a substance having a polar group such as a polyamine (PAM). Such products are sometimes referred to generically as PIBSA-PAMs. The invention also relates to methodology useful for mitigating the fouling tendencies of crude oils and the like which includes the addition of an improved fouling mitigating and/or inhibiting dispersant material thereto. Furthermore, the invention relates to improved crude oil compositions wherein fouling tendencies have been mitigated by the presence therein of improved fouling mitigating and/or inhibiting dispersant materials.
2. Background of the Invention
Crude oil is complex mixture composed of many components which vary greatly in their chemical and physical properties. The basic components of crude oils include saturated hydrocarbons, naphthenes, resins, aromatics and macromolecular asphaltenes. Crude oils are classified as naphthinic, aromatic or paraffinic, depending upon the relative concentrations of these ingredients. Asphaltenes are present in most crude oils; however, the concentration thereof may vary from about 0.1 wt % to as much as 12 wt %, depending on the origin of the crude. Asphaltenes are highly aromatic conglomerates with very high molecular weights, and the same may generally be characterized as alkyl aromatics consisting of polycondensed aromatics of six or more rings. Asphaltenes are at least partially soluble in aromatics. However, the same are generally insoluble in saturated hydrocarbons, and, as a result, asphaltenes usually exist in crude oils in the form of a suspension that is stabilized by the resin fraction which acts as a natural dispersant.
As is well known in the petrochemical industry, in order to beneficiate crude oils and produce valuable commercial products therefrom, it is generally necessary to subject the crude oil materials to distillation and/or cracking operations, or the like, wherein the crude oil materials are subjected to high temperatures. However, when crude oils, and particularly those that are deficient in aromatics and/or resins, are subjected to the high temperatures needed for processing, the asphaltenes and other undesirable carbonaceous materials become incompatible with the liquid phase and tend to flocculate and/or precipitate so as to deposit and accumulate on hot metal internal surfaces of processing equipment. This accumulation of undesirable carbonaceous materials on the internal surfaces of process equipment is often referred to as “fouling.” And fouling often causes serious operational problems such as reduced heat transfer efficiency and increased pressure drop characteristics. In fact, in some cases fouling is of sufficient magnitude to totally block flow through the equipment. Moreover, fouling often may be the cause of increased metal corrosion.
Needless to say, the fouling of process equipment such as heat exchangers and/or furnace tubes, for example, is a costly problem in refineries and petrochemical plants and the like, since the fouled equipment must be dismantled, cleaned and reassembled. Such cleaning operations are not only tedious and costly, but result in a large amount of “downtime” during which the units are not functioning.
It is known that certain dispersants of specific chemical structure can mitigate and/or inhibit fouling of process equipment by crude oils and the like. Such dispersants generally function to disperse and suspend in the liquid phase undesirable carbonaceous materials such as asphaltene macromolecules that form during heating of the crude oil. Thus, these dispersants inhibit and/or prevent the accumulation of undesirable carbonaceous materials on the internal surfaces of the equipment. Generally speaking, these known dispersants have polar atoms which may function to chelate with the undesirable carbonaceous materials to thereby assist in the dispersion of the same in the liquid phase. Accordingly, the undesirable carbonaceous materials are kept in suspension and not allowed to flocculate out for accumulation on the internal surfaces of the process equipment.
Known dispersants for mitigating fouling during processing of crude oils and the like often include a long chain hydrocarbon portion to provide solubility of the dispersant in oil and a polar functionality group providing an active site capable of chelation with undesirable carbonaceous materials such as asphaltene macromolecules, whereby the latter are kept in a suspended, dispersed condition in the crude oil. These polar functionality groups often include oxygen and/or nitrogen atoms which facilitate efficient chelation and the resultant dispersion of the asphaltene. Known dispersants may also desirably have low viscosity and good thermal stability to appropriately withstand the hostile environment in which the same are utilized.
Polyisobutylene succinyl anhydride-polyamine compounds, which are often referred to as PIBSA-PAM compounds, are well known and have been used for many years as dispersants, both for dispersing oxygenated sludge in automotive engines and mitigating fouling during crude oil processing operations. The commercially available PIBSA-PAM compounds generally have a number average molecular weight (MN) within the range of from about 500 to about 2000, a nitrogen atom content within the range of from about 1.0 to about 4.0 weight % and a total base number within the range of from about 40 to about 60 mg KOH per gram of PIBSA-PAM compound. In the past, these commercially used PIBSA-PAM compounds have been made by reacting a conventional PIB with maleic anhydride or the like using a chlorine facilitated process to produce a polyisobutylene succinyl anhydride (PIBSA). That is to say, the known PIBSA-PAM compounds are generally produced by first reacting a conventional PIB with maleic anhydride at elevated temperatures in the presence of chlorine gas. The PIBSA so produced is then condensed with a polyamine (PAM) having a plurality of polar nitrogen atoms.
The production of PIBSA using conventional PIB takes place as follows:

Conventional PIB products are generally produced using an AlCl3 catalyst, and about 65% of the molecules of the polymeric product have double bonds that are 1,2,2-trisubstituted. The remainder of the molecules of the polymeric product have double bonds that are highly substituted, internal, and relatively non-reactive. The 1,2,2-trisubstituted double bonds are somewhat reactive in a thermal, chlorine facilitated reaction with maleic anhydride, whereas the highly substituted internal double bonds are essentially non-reactive with maleic anhydride. The PIBSA products are generally of low quality with high color and considerable char. Active PIBSA yields are generally less than 70%. Moreover, when reacting conventional PIB with maleic anhydride using a conventional “ene” reaction mechanism, it is possible to attach only one maleic anhydride group to each PIB molecule. This limits the number of polar nitrogen atoms that can be incorporated into each molecule of a conventional PIBSA-PAM dispersant. As a consequence of these things, the efficiency of the conventional dispersants for purposes of inhibiting and/or mitigating fouling is limited. Methodology for producing PIBSA-PAM products where the PIBSA is prepared by reacting conventional PIB with maleic anhydride in the presence of chlorine is described in U.S. reissue Pat. No. Re. 26,330 (the “'330 reissue patent”).
More recently, processes have been developed for producing what has become known as highly reactive polyisobutylene (HR-PIB). In HR-PIB, a predominant portion of the molecules of the polymeric product have double bonds which are in a vinylidene terminal (alpha) position. Generally speaking, in commercial grades of HR-PIB, about 83 to 85% of the double bonds are in a vinylidene position. These vinylidene double bonds react readily with maleic anhydride under thermal reaction conditions to produce PIBSA products, and in general, PIBSA yields are 10 to 15% greater than when conventional PIB is utilized. Methodology for preparing PIBSA using HR-PIB as a reactant is described in European patent application no. 0 355 895 (EP '895), which also discusses the use of such PIBSA to make PIBSA-PAM. However, EP '895 does not discuss the use of the PIBSA-PAM as a dispersant for inhibiting or mitigating fouling of process equipment used for processing crude oils or the like. Moreover, the nitrogen content of the PIBSA-PAM described in EP '895 is quite low and in each case is far less than 2%.